Oxidation and silver corrosion resistant lubricants



if ma! United States Patent '0 OXIDATION "SILVER CORROSION RESISTANT LUBRICANTS Andrew D. AlibotQRoss, and James H.'Walker, Richmond, Calif., assignors to California Research (Zorporation, San Francisco, 'Calif.,- a corporation of Delaware v r a No Drawing. Filed net. 31, .1956,.Ser. No. 631,474

4 Claims. 01. est-32.7)

surfaces. 1

Generally, oils of lubricating viscosity are now Qsuhjected to highertemperatures and ,greater conditions of wear than those whichexisted only a relatively few years :ago. Such changesin lubricatingreguircmentsare duepri- .marily' to the many advances which haveoccurred in the design of automotive equipment. For example, diesel engines used in railway service are now equipped with bearings lined with pure silver metal. Also,.many auto- :mobilesvhave valve lifters which are subject to such high loads -that; the bearing surfaces operate under conditions approachingboundarylubrication. Thus, new require- :ments have ,been imposed ,on lubricating oils so that oils which ,were (satisfactory just ,a few years ago are now inadequate for proper lubrication Metal salts of, thiophosphoric acids, particularly alkaline earth metal .and zinc salts of alkyl .or alkylaryl dithiophosphoric acids, have long been used asadditives for lubricating oils. These salts have been extremely effective in inhibiting oxidation of oils and corrosion of alloy bearings, and in imparting extreme-pressure properties to oils.

Because the above-noted salts of dithiophosphoric acids cause severe corrosion of silver in engines employing silver wearing surfaces, a bi-metal dithiophosphate was developed as a lubricating oil additive to inhibit oxidation corrosion and at the same time be substantiallynoncor- .rosive to silver wearingsurfaces.

Although these bi-inetal dithiophosphates are extremely effective as lubricating oil additives to impart oxidation corrosion and silver metal corrosion resistance there- 10,111656 salts .have an unfavorable characteristic. After .lubricating oil compositions containing-these bi-metal idiathiophosphates have been left standing for a period of "time, .ascum forms on'thesurface of ;the oil. This scum :;(i.e., this film :of plastic-like substance) :becomes'so thick qdithiophosphoric acid; Fetc. a

and firm :as to be deleterious to lubricating systems in that thelines become plugged, hampering properlubrica- :ticn.

of dithiophosphoric acids can be inhibited by treating such lubricating oil compositions with carbon dioxide.

-Thus the oxidation and silver corrosion resistant oil 2,945,811 Patented July. 19, 1950 "ice It is well known that oxidation corrosion "attacks wearing -surfaces consistingof silver-'cadmi-um alloys. "How'- ever, the silver is present in the silver-cadmium-alloy in 'very minorpercentageamount1(i;e;, less than 1 The silver wearing "surfaces with which 'we are concerned herein include -wearing surfaces which contain large amounts of silver, such as'silveralloys containing'more than 50% silver, and including'wearing surfaces of sub -stantiallypure silver. l

By the use of the carbonated bi-metal dithiophosphates of this invention," non-scumming, oxidation-resistanflubricants noncorrosive to silver have been obtained.

As used herein, the term bi-metal salts of dithiophosphoric acids means the =product which is obtained by reacting an alkaline earth metal oxide'or hydroxide with a metal salt "of an ester of dithiophosphoric acid, said metals being dissimilar; "The term -car'bonated bimetal salts of dithiophosphoric acids meansthe product obtained by contacting the bi-metal' salts of dithiophos- :phoric acids=with carbon dioxide. 7 V

Bi-metal dithiophosphates are obtained by reacting alkaline earth metal oxides and/or hydroxides with metal salts of esters of dithiophos'phoric :acids' of the formula a i Ro -r s t;

*wherein R and R may be alkyl radicals containing at Lleast 8 carbon atoms, and :alkaryl .or aralkyl radicals :containing'la total of 'from 1'2 toIO :carbon atoms; and

.of Group *II of Mendeleifis iPer'iodic'Table, preferably calcium, barium, or zinc. The metal 'M is not the same .metal as the alkaline earth-me'tal of the oxide tor hydroxide :reacta'nts used in the formation :of the bimetal dithiophosph'ates. 'At :least one of the metals :of the 'bi-metal dithiophosphates is an alkalinefearth metal.

, The R radicals and the R. radicals can be :derived from straight chain or branched chain alcohols containing at least 8 ,carbon atoms, ,or"al'kylphenols, wherein the alkyl radicals contain at -least 6 carbon atoms; for example, n-octanol, Z-ethyl-hexanol, 2-propylpentanol, decanol, undecanol, dodecanol, .hexadecanol, octadecanol, hexylphcnol, deeylphenol, dodecylphenol, hexadecyl p ol, octadecylp nolr.dicetyli o lrrhenyl anol, etc.

fi mn a ster t d t qnh iiho c ac ds :which are reacted'wjith the alkalineearth metal oxides or'hydroxides are dioctyl d ithiophosph oric acids; Ldidecyl dithiophosphoric acid; didodecyl dithiophosphoric acid; dihexa- .decyl =dithiophosphorie acid; dioctadecy'l dithiophosphoric acid; di-(decylphenyl) dithiophosphoric acidydi- :(amylphenyl) rdithiopho sphoric acid; di(dodecylphenyl) .ImproYed oil solubility of the resulting bi-metal dithio- 41 1 .is-tob ained when the alkaline earth'metal :QXidG ,(or rhydroxide) ;,:reactant .is aa oxide (or Phyd de), -the, met l salt .of dithi phosphoric acid is va .zinc salt .of estersof wdithiophosphoric acidgfiud wherein each of the ester ra (ta, the R and R o th ,formula Jhr'eintibote) are ,derived from alcohols ,orialky lphenols containing not less than 12 carbon atoms, and not more than25, carbon atoms ,(i-eait istpreferred that the-total number of carbon atoms in the ester radicals is from=24*t'o-5 0). J 1

"Fol-purposes 'ofsimplificati'on, the metal or the alkaline earth metal oxide and hydroxide reactants will be termed secondary metal," and the metal of-th'e dithiophosphate reactant will be termed primary 'dithiophospha temetah" These bi-metal salts of esters of dithiophosphoric acids have molecular weights of such magnitude as to indicate the formation of complex polymerie type compounds. Molecular weight data for these compounds, as determined by sedimentation rates in an ultraeentrifuge,-show that themolecular weights are in the range of'l50,000 to 550,000. I

Suitable base oils for the compositions of this invention include a wide variety of lubricating oils such as naphthenic base, parafiin base, and mixed base mineral oils; synthetic oils, e.g., alkylene polymers, such as polymers of propylene, butylene, etc., and mixtures thereof; alkylene oxide type polymers; dicarboxylic acid esters; liquid esters of phosphorus, liquid esters of silicon (including polysiloxanes); and alkyl aromatic hydrocarbons. The above base oils maybe used individually as such or in various combinations (wherever miscible or whenever made so by the use of mutual solvents). The carbonated bi-metal salts of estersof dithiophosphoric acids are used in lubricating oils in amounts su-fficient to inhibit oxidation thereof; that is, amounts of 0.25% to 20%, by weight, preferably from 1.5% to by weight. Stated in other terms, the amounts of these carbonated bi-metal dithiophosphates may beexpressed as millimols per kilogram of finished oil, based on the phosphorus content. That is, the amount of bi-metal dithiophosphate is expressed as millimols of phosphorus per kilogram of oil ('i.e., mM./kg."). Expressed .in such terms, the amount of .bi-metal salts of esters of dithiophosphoric acids used in lubricating oils can be from 1 millimol to 50 millimols of phosphorus .per kilogram of finished oil, preferably from14 millimols to 25 millimols.

-In the preparation of the bi-m'etal salts of esters of ,dithiophosphoric acids, the monometal salts of esters of dithiophosphoric acids of the prior art can be prepared ..by methods known heretofore. For example, a' mixture of the desired alcohol or alkylphenol and phosphorus pentasulfide is reacted with or without a solvent (e.g., petroleum naphtha) at 100 F. to 200 F. until the di- "thiophosphoric acid is formed. .The crude acid mixture is then filtered to remove unreacted phosphorus pen- .tasulfide, after which the resulting acid is neutralized with a metal oxide. (e.g., zinc oxide) to form the metal dithiophosphate. Such simple metal salts of esters of dithiophosphoric acids can also be prepared by reacting the (e.g.,,barium-zinc diester dithiophosphates) are prepared by reacting a metal diester dithiophosphate with an alkaline earth metal oxide (or hydroxide) in a solvent (e.g., a lubricating oil), followed by heating to a temperature ranging from 200 F. to 450 F. (preferably from 250 F. to 375 F.), and filtering the resulting admixture.

The carbonated bi-metal dithiophosphates of this invention are obtained by contacting the above-described bi-metal salts of dithiophosphoric acids with carbon dioxide. The carbonation can be accomplished by bubbling carbon dioxide through a solution of a bi-metal di -thiophosphate (e.g., aiubricating oil solution of a bimetal dithiophosphate) at temperatures ranging from about 60 F. to about 300 F. It ispreferable to prepare 'aconcentrate of thebi-metal dithiophosphate in oil; for example, from about'l5% to about 70%, by weight,

of the bi-metal dithiophosphate in alubricating oil, and

"bubble the earbondioxide through the concentrate; or

treat theconcentrate-with carbon dioxide as described hereinbelow.

The following examples illustrate theprep arationof lubricating oil compositions containing such -C rbonated 4 EXAMPLE l.PREPARATION OF BI-METAL DITHIOPHOSPHATE A mixture of 5 pounds (0.032 pound mol) of barium oxide (92% purity) and 125 pounds (0.0625 pound mol) of a zinc di(alkylphenyl) dithiophopshate (containing 3.27% zinc, 3.0% phosphorus, and 5.78% sulfur, and wherein the alkyl radical is derived from propylene polymers having an average of 12 carbon atoms) was incorporated in a California solvent-refined paraflin base oil havinga viscosity of about 140 SSU'at 100 F. The whole mixture was'heated in -a kettle with agitation at BOO-310 for a period of 1.4 hours. 79 pounds (0.245 pound mol) of barium hydroxide octahydrate (98% purity) was then charged at the rate of 20 pounds per hour while the temperature was maintained at 300 'F. to 310" F. The barium-to-zinc mol ratio of this charge was 4.43 to 1.0. The pH of the charge (determined in a solvent consisting of 40%, by volume, of ethyl alcohol; 40% ethyl ether; and 20% water) increased from 4 to 13+. The whole mixture was agitated at 300 F. for another hour, with nitrogen flowing through the bottom of the bottle to remove residual moisture. This was followed by a final drying period of 30 minutes at 300 F. under a vacuum of 25 inches of mercury. To this mixture was added 5 pounds of Celite filter aid, after which the mixture was cooled to 250 F. and filtered.

The resulting product analyzed 1.76% zinc, 16.73% barium, 1.63% phosphorus, and 3.26% sulfur.- The mol ratios based on zinc, as one, were as followsz' barium, 4.52; phosphorus, 1.95; and sulfur, 3.78. The viscosity was 3838 SSU at 100 F., and 155 SSU at 210 F.

The barium-zinc di(alkylphenyl) dithiophospha-te product thus formed was isolated from the lubricating oil concentrate as follows: 100 grams of the above lubricating oil concentrate was dissolved in 100 ml. of benzene. 300ml. of C.P. acetone was added to precipitate out the compound. The solid fraction precipitating out was separated and redissolved in 100 ml. of benzene and reprecipitated with 300 ml. of CF. acetone.

Table I hereinbelow sets forth the analysis of the reprecipitated solid, again using zinc content as the base for determining the mol ratio.

The bi-metal dithiophosphates can be carbonated at atmospheric. pressures and ambient temperatures (e.g., room temperature; i.e., about 68 F.), or at pressures as high as, or higher than, 100 p.s.i. and temperatures as high as, or higher than, 300 F. At the higher temperatures, it is beneficial to use lower pressures; that is, pressures rangingfrom about atmospheric pressure'to about 50 to about 75 p.s.i. For example, when the temperature is approximately 300 F. or higher, it is preferable to use pressures from about'atmospheric pressure to 50 p.s.i.

When it is desirable to use lower temperatures, that is, temperatures from about 60 F. to about 225 F., higher pressures may be used (for example, pressures as high as p.s.i., or higher).

For purposes of this invention, it is preferred that the carbonation of bi-metal dithiophosphates be accomplished at temperatures ranging from about 60 F. to about 225 F., and pressures from about atmospheric to about. 50 p.s.i. 1

The following examplesillustrate the preparation of carbonated bi-metaldithiophosphates...

QB BI-METAL DITHIOPI-IOSPHATES 'A FMOSP PRESSURE;

' iln g rams? of an oil? Barman (at California solvenf refined paraihhfibase oi having a 'viscosity' ofab'o'ut' 1'40 SQU at 100 F.) containiirg 6o- -*2%:,"5y weight; of the .dithiophos'phate or. Example 1}, hereinabove; was cai honated" by"adtlingDryIcetheretoat a temperature or F. The whole mixture was-vigorously agitated for about 2 hours. There was a constant excess of carbon dloiridbiiv coarser 'witli the oil= liquid at? all tim'esi HUMBLE iii-PREPARATION OF CARBONATED H B'IMETALJDI IiI-IIQPHOSPHATE 100 PLSYI. -i 1500 grams? oft art. oi'l solutioni (aw California solvent refined: paraffin: base; oili havinga: viscosity: of about 140 SSU: at 100. 1 containing: 60;*:2%., I by weight; of the: bivn'netal. dithiophosphate; of: Example: 1,; hereinabove, were charged to a: closed: vesselof 250.0: capacity; The vessel was connected to -a. soureeioffcarbom dioxide, and the=cai=bon dioxide wa's pressured; into the closed vessel, s'o -that-i wconstantpressureof: 1Q0-p.s.i;g. was maintained. Thereactants;were-constantlyagitated at 325310" F. for aperiod ct -2 hours. The reaction-product; was analyzed astfollowsti.

. I Table H Percent-By M01 Ratio .Weizht '4Z-'-PREPARATIGN on CARBO'NAIED BI-METXI. D'ITHI OPHOSPHATE'S AT 50 PiSll.

1000 grams of an oil solution (a California solventrefined paraffin base oil having a viscosity of about 140 SSU at 100 F.) containing 60i2%, by weight, of the bi-metal dithiophosphate of Example 1 hereinabove, were charged to a closed vessel having a capacity of 2500 ml. The vessel was connected with a source of carbon dioxide and the pressure within the vessel was raised to 50 p.s.i.g. by a charge of the carbon monoxide. The contents of the vessel were vigorously agitated at 225 F. for a period of 2 hours. A constant pressure of 50 p.s.i.g. was main tained by the carbon dioxide. The reaction product analyzed as follows:

37 grams of an oil solution (60%, by weight) of the bi-metal dithiophosphate of Example 1, hereinabove, was allowed to stand in a 250-ml. beaker at room temperature for four days, during which time the surface of the oil became coated with a heavy plastic-like film. 37 grams of an oil solution (60%, by weight) ofthe carbonated bi-metal dithiophosphate of Example 3 was placed in a 250-ml. beaker and allowed to stand for 4 days at room temperature. The surface of this oil remained clear and free from any scum or plastic-like film formation.

The carbonated bi-metal dithiophosphates are particularly effective as lubricating oil additives when the mol ratio of the Secondary metal to the primary dithiophosphate metal is from about 3.7 to l to about 4.6 to 1 (i.e., has a value from 3.7 to 4.6).

Table IV hereinbelow presents data showing the effecbase oil, the test conditions; etc2,, whichwere used are described as follows: g V ,7 W

The. base oil-..in each" instance. wasrav 60 VJ; SAE 40 California. base oil containing,4-millimolszof a petroleum sulfonate wherein the petroleum-radical was. obtained fromta. California; paraflin'haseoil. having; a cosity of 480 SSU at F. To "this base oil was. then incorporated the additive of the table in the: amounts specified-therein; V i I The bi-metal dithiophosphates were prepared accord.- ing. to the. process. described in- Example 1,. hereinabove, by reacting barium oxide and barium; hydroxide with: a zinc di(alkylphenyl) dithiophosphate, wherein the alkyl radical was obtained from. polypropylenes containing, an average of. 12 carbon. atoms. .The carbonated b't-metal dithiophosphates were prepared according to the process described in Example 2 hereinabove.

The silver strip test which was used is described as follows: I

A silver metal strip having the dimensions of 2% inches by inch by inch was first cleaned with a wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly polished silver strip was then placed in a 600 m1. beaker in such amariner that the strip was" completely immersed when 300"g rams of theoil being tested was poured into the beaker; The oil' w'as'stiir'ed at'a temperaturenf 300 F1 for 20" hours; at which time the silver"strip'was removed and cleaned; first with chloroform; then with petroleum ether. The appearance of the strip' was noted. strips'whichhad been'severely attackedwere quite black. The tested silver stripwaswashed inf'f5%- aqueoussdlh tion of potassium cyanide for about 5 minutes to remove the sulfide film adhering to the strip. After the strip had been washed with potassium cyanide and dried, it was weighed. The difference in weight ofthe original strip and the strip after the potassium cyanide wash was noted and recorded as the weightless due to corrosion.

The copper-lead strip corrosion'tests were run as follows: A polished copper-lead strip (obtained from a commercial bearing) was weighed and immersed in 300 ml. of test oil contained in a 400 ml. beaker. The test oil was maintained at 295 F. under pressure of one atmosphere of air and vigorously stirred with a mechanical stirrer. After 2 hours, a catalyst was added to provide the following catalytic metals (all percentages being by weight):

The test was continued for 20 hours, after which the copper-lead strip was removed, rubbed vigorously with a .soft cloth, and weighed to determine the weight loss.

Table IV Additive (mM./kg.)

(Based on Metal) L-4 Engine Silver Strip Test, Weight OiiNo. Corrosion, Loss Mg. per

Uncarbonated Carbonated Mgs. Loss Whole Bear- Bi-metal Bi-meta] lug Dithio- Dithiophosphate phosphate 7 Although thecompositions'of the present invention have been described above as being primarily useful as internal combustion engine lubricants, the additives herein are suitable for use in gear lubricants, ice machine oils, instrument oils, constituent oils for grease manufacture, turbine oils, and the like.

In addition to the additives noted hereinabove, the lubricating oils of this invention may contain other oxidation inhibitors, grease thickening agents, color correctors, extreme pressure agents, oiliness agents, gel modifiers, etc.

We claim: 1

1. A lubricating oil composition consisting essentially of a major proportion of an oil of lubricating viscosity and a carbonated bi-metal salt of a dithiophosphoric acid in an amount of about 0.25% to 20%, by weight, wherein, said bi-metal salt is prepared by reacting a metal material selected from the group consisting of barium oxide and barium hydroxide with a zinc dithiophosphate of the formula:

wherein R and R? are hydrocarbon radicals selected from the group consisting of alkyl and alka ryl radicals, each radical containing from 12 to 25 carbon atoms, wherein said reaction is at a temperature of 200 F. to 450 F., followed by filtration, and oarbonating at temperatures from.60 F. to 300 F., wherein said carbonated bimetal salts of diester of dithiophosph oric acid have a molecular weight ranging from 150,000 to 500,000, and

8 wherein the mol ratio of barium 'to zinc ranges from 3.711 to 4.6:1.

2. The lubricating oil composition of claim 1, wherein the zinc dithiophosphate radicals are alkaryl radicals, each containing from 12 to 25 carbon atoms.

3. The lubricating oil composition of claim 1, wherein said zinc dithiophosphate is a zinc alkaryl dithiophosphate wherein each alkyl radical is derived from propylene polymers having an average of about 12 carbon atoms.

4. A lubricating oil compositioncon sisting essentially of a major proportion of an oil of lubricating viscosity and a carbonated bi-metal salt of a diester of a dithiophosphoric acid in an amount of 0.25% to 20%, by weight, wherein said bi-metal salt is prepared by reacting a metal material selected from the group consisting of barium oxide and barium hydroxide with a zinc di- (alkylphenyl) dithiophosphate, wherein said alkyl radicals are obtained from propylene polymers having an average of about 12 carbon atoms, wherein said reaction is at a temperature of 200 F. to 450 F., followed by filtration, and carbonating at temperatures from F. to 300 F., wherein said carbonated bi-metal salts of diester dithiophosphoric acid have molecular weights ranging from 150,000 to 500,000, and wherein the mol ratio'of barium to zinc is from about 3.721 to about 4.6: 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,616,924 Assefi et al. NOV. 4, 1952 2,767,164 Assetf et al. Oct. 16, 1956 FOREIGN PArENTs v 723,133 Great Britain Feb. 2,, 1955 1,110,712 France Oct; 19, 1955 

1. A LUBRICATING OIL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF AN OIL OF LUBRICATING VISCOSITY AND A CARBONATED BI-METAL SALT OF A DITHIOPHOSPHORIC ACID IN A AMOUNT OF ABOUT 0.25% TO 20%, BY WEIGHT, WHEREIN SAID BI-METAL SALT IS PREPARED BY REACTING A METAL MATERIAL SELECTED FORM THE GROUP CONSISTING OF BARIUM OXIDE AND BARIUM HYDROXIDE WITH A ZINC DITHIOPHOSPHATE OF THE FORMULA: 